[Info-vax] Compatibility and 64-bit

[Stephen Hoffman]

On 2015-03-16 00:44:45 +0000, JF Mezei said:

> On 15-03-15 18:59, Stephen Hoffman wrote:
> 
>> Everything is defined at compile time, certainly.  On OpenVMS Alpha,
>> all virtual addresses are 64 bits, and always have been.  That means
>> that pointers are either 64-bit addresses, or they are 32-bit addresses
>> that get sign-extended to 64-bit addresses.
> 
> If 32 bit addresses are used in the code, does it get extended to 64 bit
> by using different machine instrunctions that fill the missing 32 bits,
> or is there some sort of "switch/flag" in the process that tells the CPU
> to only look at first 32 bits and sign extend it to 64 before making the
> request to the virtual memory system ?

CC/MACHINE/LIST=mumble.lis file.c/NOOBJECT some handy C code, and have 
a look at <http://download.majix.org/dec/alpha_arch_ref.pdf> for 
details.


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